1. Field of the Invention
The present invention relates to a nuclear magnetic resonance (NMR) device, and more particularly to a low temperature probe for the NMR.
2. Description of Related Art
In the NMR device, since a nuclear magnetic resonance signal of a hydrogen nucleus has a better sensitivity than the other nuclei, the NMR device is used as a tool for analyzing a molecular structure of an organic matter. In an advanced life science research and a biological field, it measures a protein having a large molecular weight and is used for researches such as a search and analysis of an interaction between structures of molecules corresponding to a feature of the NMR and with respect to the other molecules, in addition to the molecular structure. In order to execute a structural analysis of the protein at a high speed, it is absolutely necessary to make the NMR device highly sensitive. The NMR device in recent years generates a high magnetic field by utilizing a superconducting magnet, and can achieve a high sensitive detection by cooling a detection coil.
Patent documents 1 (JP-A-2003-329755 and Patent document 2 (JP-A-2003-329756) describe an NMR device characterized by a horizontal insertion type probe by arranging a solenoid type receiver coil in a horizontal magnetic field magnet. In accordance with this structure, a signal detecting efficiency is more excellent in comparison with a saddle type receiver coil.
The NMR probe in the patent documents mentioned above is not sufficient about the cooling structure of the receiver coil for enabling the high sensitive measurement. When actuating the low temperature probe, the receiver coil is cooled, however, a probe container is not cooled but is kept at a room temperature.
In a device for executing a general very low temperature cooling, an internal portion of the container of the device is made vacuum, and a heat transmission by a gas is adjusted. All the same, since a heat is transferred to the internal portion due to a radiation heat, the structure is made such as to reduce the radiant heat, and employ a heat radiation shield in which a temperature is kept at about 70 K to 100 K, a reflector material, and a laminated heat insulating material installed in an outer side thereof and formed by laminating heat insulating materials in multilayer. It is possible to limit the transfer of the heat due to the heat radiation which is in proportion to a difference between biquadrates of the temperatures to 1/100 by changing a surface visible from the internal very low temperature 100 K or smaller from about 300 K corresponding to the room temperature.
However, in order to use the heat shield technique as it is, the portion around the coil in the low temperature probe is hard due to a spatial restriction. Since a detecting sensitivity of the receiver coil is more improved in accordance that the receiver coil is closer to a sample, it is preferable to make a gap between an outer wall of a sample space and the receiver coil smaller, and the gap is set to be equal to or smaller than 1 mm.
Particularly, there is generated the other problems in the low temperature probe in connection with the cooling. Most of the constituting materials of the low temperature portion of the low temperature probe generates a contraction by being cooled. For example, a copper and an aluminum used for improving a heat conduction generates the contraction at 0.3 to 0.4% of its length at a time of being cooled to a very low temperature from the room temperature. Accordingly, a displacement is generated in the coil and the gap between the receiver coil and the sample is increased, thereby deteriorating the sensitivity.
The present invention is made by taking the problem of the prior art mentioned above into consideration, and an object of the present invention is to provide a low temperature probe which can efficiently cool a coil in a narrow space, has a small thermal noise and can execute a high sensitive measurement, and an NMR apparatus using the same.